For starting an internal combustion engine, it is conventional to use an electric starter which, during the starting phase, is operatively connected by means of a starting pinion to a toothed ring of a flywheel which is assigned directly to the crankshaft of the internal combustion engine. Said electric starters have a torque characteristic which is comparable to a series-wound machine, wherein from a maximum possible torque, an output torque decreases sharply with rising rotational speed.
DE 32 41 079 A1 discloses a starting device, which comprises two starters, of an internal combustion engine, which starters are in each case activated together during all starting processes. In EP 0 406 182 B1, the starting device comprises a boost circuit, by means of which a higher voltage can be generated for starting, which higher voltage briefly generates higher currents in the motor-driven electric machine, and thereby increases the torque. Said solution has the disadvantage that, at low temperatures, the slipping tendency of the belt drive increases. Furthermore, the charging time of the starting battery is a problem, as a result of which it is not possible to carry out starting processes one after the other at short intervals.
DE 100 45 143 A1 discloses a tensioning system, which comprises two pulleys, of a traction mechanism drive, which tensioning system can be used for a starter-generator concept. In the starter-generator, a change in direction of the torque which is introduced into the traction mechanism drive takes place as a function of the operating mode. On account of the alternately-directed torque, the traction mechanism drive requires a tensioning system which comprises two pulleys and which pre-tensions in each case the idle strand, which is assigned to the starter-generator, of the traction mechanism with a sufficient resilience. The tensioning system comprises two lever arms which are connected to one another in a rotationally rigid fashion and on which separate pulleys are arranged. In this way, in the operational state of the internal combustion engine, a reaction is generated at all times between the tensioning rollers assigned to the idle strand and to the tension strand. A deflection of the pulley which is assigned to the tension strand generates a corresponding counter-torque, as a result of which a support force of the pulley which is assigned to the idle strand is increased.